Functional traits can be defined as the characteristics of organisms that allow them to persist in a givenenvironment. The functional approach of Plant Ecology allows studying the interactions between individualswithin a community, and the interactions of these individuals with their environment for a largenumber of species. Thus, the functional approach can be connected to issues related with functional strategies,assembly rules and species distribution along the landscape, as well as ecosystem processes. Theoverall aim of this Thesis is to better understand the strategies developed by different species to persist ina given environment as well as the assembly rules of Mediterranean woody plant communities, within theconceptual framework of functional ecology. To address these broad objectives, we developed differentapproaches, at different scales of study, making up a total of 5 chapters (plus Introduction and general Discussion):The chapter 2 is focused at leaf level. In this chapter we studied the leaf mass per area (LMA) variationon 34 (20 evergreen and 14 deciduous) woody plant species selected along a local environmental gradientin Sierra Morena (south Spain). LMA is a morphological leaf trait widely used as a good indicator of plantfunctioning; however, the structural components which underlie the interspecific variation in LMA arestill poorly understood. This study showed that variation in LMA was due to variation in both leaf thicknessand density. In turn, leaf thickness variation was positively related with mesophyll. In evergreen species,other anatomical tissues (such as epidermis, vascular tissue and air spaces) were found positively relatedas well. In addition, different environmental conditions may impose different selective pressures onplants species with certain leaf traits, appearing species with higher values of LMA and leaf density indrier areas.In the chapter 3 the functional coordination of leaves, stems and root traits on 38 woody plant species selectedalong a local environmental gradient (Sierra Morena) is analyzed. Plants, like so many organisms,have several organs that are specialized for different functions. Thus, the main role of leaves is light capture,while roots are related with soil water and nutrient uptake, and stems supply these resources to leaves.According with their functional diversification, differences among organ characteristics could be expected.Currently, an intense debate in plant ecology exists about the coordination among leaf, stem and roottraits. Understanding this issue could help to bring some clarification about how plants function, as well asto discern the potential effects of environmental changes (such as those derived from climatic change predictions)on plant community structure. This study revealed a high degree of functional coordination betweentraits belonging to different plant organs. For example, species with higher stem density showed alsohigher values of leaf and root density. These results suggest the existence of an “economics spectrum” atwhole plant level in Mediterranean woody plant species. On the other hand, the same coordination betweentraits was found at community level, with stronger relationships at this hierarchical level. In addition,we found that the distribution of plant communities along the soil moisture gradient followed a clearpattern. Thus, drier areas were dominated by communities with a higher dominance of species associatedwith a more conservative use of resources, while wetter areas were dominated by species with a more acquisitivestrategy. However, the general trend of coordination between traits of different organs becameweaker or disappeared at a lower spatial scale, when considering groups of species belonging to environmentallysimilar sites. This suggests that the diversification of strategies within communities was not relatedto the economics spectrum at a lower spatial scale.The chapter 4 is mainly focused on the factors that govern the functional structure of plant communitiesalong a local environmental gradient (in Sierra Morena mountains). Thus, the functional approach allowsus to discern the filtering mechanisms and the distribution patterns that take place in these communities.The functional trait variation of nine woody plant communities was analysed along a wide soil resourcegradient. For this approach, several functional traits at both aboveground (plant size, specific leaf area,leaf and stem dry matter content, etc.) and belowground (root dry matter content and specific root length)level were quantified in 38 Mediterranean woody plant species. A new practical method to quantify the...